It has been known that bis(fluorosulfonyl)imide salt ((FSO2)2N.M, wherein M is Li, K, NH4, or the like) is a useful anion source for ion electrical conducting materials and ion liquids. Also, it has been known that fluorosulfate is a useful compound used for ion electrical conducting materials and fire-retardant materials. In addition, it has been known that bis(fluorosulfonyl)imide onium salt is a useful ionic compound as an ionic liquid.
As a method for producing bis(fluorosulfonyl)imide, the methods disclosed in NPL1 and NPL2 have been known. More specifically, in NPL1, a method, in which urea (CO(NH2)2) and fluorosulfonic acid (FSO3H) are mixed first, and then the resulting mixture is heated, allowing the chemical reaction between them to proceed, is disclosed. In this reaction, the chemical reaction represented by the formula (1) below proceeds, producing bis(fluorosulfonyl)imide, ammonium hydrogen sulfate (NH4HSO4), hydrogen fluoride (HF), and carbon dioxide (CO2).3FSO3H+CO(NH2)2→(FSO2)2NH+NH4HSO4+HF+CO2  (1)
By distilling under reduced pressure during the reaction, a mixed liquid consisting of the newly produced bis(fluorosulfonyl)imide and fluorosulfonic acid is fractionally distilled. By distilling the obtained mixed liquid further, bis(fluorosulfonyl)imide can be recovered.
In NPL2, a method, in which bis(chlorosulfonyl)imide ((ClSO2)2NH) and arsenic trifluoride (AsF3) are reacted, is disclosed. In this reaction, the chemical reaction represented by the formula (2) below is allowed to proceed, producing bis(fluorosulfonyl)imide and arsenic trichloride (AsCl3).3(ClSO2)2NH+2AsF3→3(FSO2)2NH+2AsCl3  (2)
After the reaction, the newly produced bis(fluorosulfonyl)amide is dissolved in dichloromethane. The fraction of the newly produced bis(fluorosulfonyl)amide contain fluorosulfonic acid as an impurity. The contaminating fluorosulfonic acid can also be dissolved in dichloromethane. By adding NaCl to the dichloromethane dissolving bis(fluorosulfonyl)amide and fluorosulfonic acid, the chemical reaction represented by the formula (3) below is allowed to proceed, producing sodium salt of fluorosulfonic acid (FSO3Na) and hydrogen chloride (HCl). Bis(fluorosulfonyl)imide can be recovered by distilling away dichloromethane, after removing the precipitated sodium salt of fluorosulfonic acid.FSO3H+NaCl→FSO3Na+HCl  (3)
As a conventional method for producing bis(fluorosulfonyl)amide salt, a method, in which bis(fluorosulfonyl)imide is produced by the methods disclosed in NPL1 and NPL2, and is neutralized by an alkaline compound after dissolving the recovered bis(fluorosulfonyl)imide in water or the like, has been known, as described in NPL3.
As a conventional method for producing fluorosulfate, a method utilizing the chemical reaction represented by the formula (3) has been known. In the method, the bis(fluorosulfonyl)imide produced by the methods disclosed in NPL1 and NPL2. The bis(fluorosulfonyl)amide fraction containing fluorosulfonic acid is dissolved in a solvent, such as dichloromethane or the like, and reacted with NaCl, producing fluorosulfate.
As a conventional method for producing bis(fluorosulfonyl)amide onium salt, a method, in which bis(fluorosulfonyl)imide is produced by the methods disclosed in NPL1 and NPL2, and an onium compound is added to the bis(fluorosulfonyl)imide after dissolving the bis(fluorosulfonyl)imide in water or the like, has been known.